This 3 minute video shows takes you inside the brain of Fritz, the Robot Puppet.

Inan earlier post we talked to Kerwin Lumpkins about Fritz, a Robot Puppet that he designed with colleague Steven Gertner. Kerwin used Solidworks to model Fritz. Here's a tour that he produced for ENGINEERING.com.

Steven and Kerwin thought Fritz would take about 2 months to design, but the project actually took 6 months. The hardest parts were:

Eyelids. The eyes have to move X and Y, so you can't just put an axle through them. Instead, they needed a universal joint and then the eyelids have to fit around that and not interfere. The spacing is really challenging.

Their early eyelid design worked, but was too slow. Real eyelids blink fast, so they redesigned for speed rather than torque. When they changed something in their CAD model by 1/8", it caused interference in 8 different places, which in turn cause follow-on interferences. They then needed another month to make the eyelids manufacturable.

Fritz with hair band mouth

Lips. The first idea for the lips was a hair band, or "Scrunchy".

Unfortunately, they found that it would slide around if you didn't rigidly connect the corners. And it would change shape when the corners were rigidly connected, so it didn't look mouthlike.

They also found that the resistance from the rubber would unbalance the servos. Kerwin and Steven tried surgical tubing, but the servos weren't powerful enough to stretch the tubing. Then rubber bands, but they didn't look lifelike.

One of the challenges of designing a human proportion robot is to steer clear of the "uncanny valley", the effect of a design that is close to, but not close enough, to lifelike.

So their design had to look clearly not-human. To meet that objective, they finally settled on a metal spring. It works very well, but clearly looks mechanical.